An ore body, which is of a payable grade sufficient to support an underground mining operation, can be accessed via shafts or inclines. To further facilitate access to the ore body horizontal excavations called levels are excavated horizontally off the shafts or inclines, whereas stopes are excavated generally perpendicular to the levels.
Mining operational safety requires that when a workman is underground, i.e. standing in the stopes or on various levels with a footwall under his feet and with the hanging wall hanging above him, proper measures need to be in place to maintain the stability of the excavated areas and to prevent ground from collapsing onto the workman. In the past, a variety of methods and devices have been derived in an attempt to address this need, one of which is an anchor bolt or so-called ‘rock bolt’ forming part of a rock anchoring system. A rock anchoring system transfers load from the unstable exterior of the hanging wall to the confined, and more stable, interior of the rock mass surrounding the hanging wall. Rock bolts are thus not only used extensively for slope or level stabilization, but also provide tie back and tie down positions.
It is known that a rock anchoring system can be secured in the interior of the rock mass with a mechanical means and/or epoxy means of establishing a set. As such, holes are drilled into the hanging wall so as to accommodate bolt shafts of the rock bolts. When an epoxy resin is used, the resin grout develops a bond superior to that developed by, for example, a cement grout. Fast setting of the resin grout is then necessary to allow transfer of load to the rock formation within minutes after installing the bolt shaft into the drilled hole with epoxy resin grout therein.
Ubiquitous rock anchoring systems typically include a rock bolt having a bolt shaft, of which a screw threaded portion projects from a rock surface of the hanging wall when a major portion of the shaft is set within the drilled hole; a bearing plate/washer which is fitted over the bolt shaft; and a nut which is screw threaded onto the screw threaded portion of the bolt/shaft. The nut bears against the bearing plate which, in turn, bears against the rock surface of the hanging wall.
In some instances the holes drilled into the hanging wall are up to three meters long. Accordingly, bolt shafts of three meters and longer are required to fit into, and protrude from, these holes. The bolt shafts are further manufactured from solid metal or metal alloys and, thus, have a considerable weight which hampers the ability of a workman to move or carry the rock bolts around in the levels or stopes.
A further problem with existing rock anchoring systems is that they tend to loosen from their set positions in the hanging wall, especially when rock blasting operations occur nearby.
As such, it would be advantageous to introduce a rock anchoring system having features permitting it to be easily handled by workmen and the like in an underground environment. It would also be advantageous to introduce a rock anchoring system having features which improve the traction of a bolt shaft of such a system in the rock mass surrounding the hanging wall or the traction of the bolt shaft in the epoxy means.